Iran's President Hassan Rouhani said Wednesday that the United States' r
eaction to floods that killed dozens of people had revealed Washington's "vicious" nature.
At least 76 people have died after torrential rainfall which has also caused billions of dollars worth of damage since March 19.
Iran's Red Crescent has repeatedly complained that US banking sanctions re-imposed last year make it impossible to receive donations from outside the country.
Washington "always claimed that it is on very good terms with the people of Iran (and) it is the Iranian government that it has a problem with," Rouhani said.
But by blocking aid to the Red Crescent, the US had given lie to that claim, he said.
"The heads of the American regime have revealed their true vicious and inhuman nature," he said at a cabinet meeting screened live on state TV.
The International Federation of Red Cross and Red Crescent Societies have estimated two million people need humanitarian aid following "the largest disaster to hit Iran in more than 15 years".
The floods were a "historic test" for the American leadership, Rouhani said.
US President Donald Trump last year withdrew Washington from a multilateral agreement on Iran's nuclear programme, later re-imposing sanctions focusing on oil exports and financial transactions.
Iran's Foreign Minister Mohammad Javad Zarif has accused the US of "economic terrorism", saying its unilateral sanctions were impeding aid efforts to flood-stricken cities.
Iran has received material aid from neighbouring countries such as Pakistan and Kuwait as well as from Germany, France and Japan.